Note: Descriptions are shown in the official language in which they were submitted.
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BITUMEN PRODUCTION ~HROUG~I A ~ORIZONTAL WELL
_
- (D#77,400-TCRL-002-2-F)
BACKGROUND OF THE INVENTION
This invention relates to an apparatus and method
therefor, which includes the deep boring into a formation for
the purpose of extracting hydrocarbon fluids from the earth.
More specifically, the invention relates to a method for
thermally treating a subterranean formation to reduce the
viscosity of fluids which are retained in the formation,~
thereby enhancing the extraction of the hydrocarbons. The
latter is achieved through the use of means to control the
movement of the thermal treating reaction, to most effectively
sweep a productive layer.
The vast majority of heavy oil reservoirs such as tar
sand formation, lie 50 meters under the surface of the earth
and therefore must be tapped through the use of in situ
technology. Examples of heavy oil reservoirs include those
located at the Athabasca and Cold Lake regions of Canada. In
the bnited States the Edna and Sisquoqe are located in
California as well as in the tar sand triangle in Utah.
The high viscosity of hydrocarbon having a density
which is between 10 and 20 API, characterize all the above
mentioned deposits and substantially all tar sand reservolrs.
The heavy oil found in such reservoirs commonly referred to as
bitumen, contained in tar sands, is usually immobile at
reservoir temperatures.
In the particular situation of tar sand reservoirs
such as in the Athabasca region of Canada, the reservoir
temperature is approximately 7C. The viscosity of the viscous
oil is above l million centipoises. In such a condition for
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all practical purposes, the hydrocarbon is considered as being
formed of solid matter.
Another important feature of many tar sand reservoirs
is the nature of the solid matrix which is generally comprised
of a fine, unconsolidated sand with the median between 100 and
200 um containing the heavy, viscous oil.
Attempts to recover heavy oil from a tar sand
formation have to deal with at least two major problems. These
include the reduction of the oil's viscosity, and the movement
of solids such as unconsolidated sands.
.
One of the most successful-y applied practices for-
recovery of the heavy oil from tar sand is through in situheating or stimulation.
The efficiency of the heating process is enhanced by
the increase of net convection, or the amount of heating fluld
which can penetrate the tar sand formation. As a rule, the tar
sand's formation is initially saturated with an 80 to 90% high
viscosity oil; only 10 to 20% saturated with gases and water.
For most of the tar sand reservoirs and particularly
for. ones with low and medium temperatures, an initial net
convection of the heating fluids into the reservoir cannot be
readily determined. Any increasing of the injection pressure
of the heating or stimulating fluid carries with it the
likelihood of fracturing the reservoir in an undesirable
direction out of the tar sand formation. This circumstance is
undesirable since the stimulating fluid will be of no further
use.
To control the injection of heating fluids into the
formation, it has been proposed to drill inclined and/or
horizontally deviated wells. The latter will conduct the
heating fluids, and/or additives directly into the heavy oil
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formation.
The present invention provides an improvement in
means for producing bitumen and viscous hydrocarbon from tar
sand and other formations in which the hydrocarbon is released
through thermal stimulation. Examples of such wells are
disclosed in U.S.P. 3,913,672, J. C. Allen et al;
U.S.P. 3,908,762, D. A. Redford. In the methods there taught,
naturally occurring high permeability breaks or those formed by
means of conventional hydraulic fracturing and propping are
proposed as a solution for penetrating the tar sand formation.
A diversified, simultaneous injection-production
method can be achieved from a single well as disclosed in
U.S.P. 3,813,~71, D. A. Redford et al. This latter concept is
further disclosed in U.S.P-. 4,088,188, R. H. Widmyer.
In the above described methods, at least one
production well is completed to provide a separate path from
the surface in order that a treating fluid can be introduced
into a portion of an underlying hydrocarbon productive
formation. The aqueous heating fluid can be injected into a
portion of the formation adjacent to the production well on a
timed progress basis. Thereafter, continuous injection of the
aqueous heating fluid into the formation can also be utilized.
Toward the further production of heavy hydrocarbons
from environments such as tar sands, there are known processes
which utilize horizontal or long deviated wells to recover
heavy oil from tar sands. These however are subject to at
least two major drawbacks. The latter include the control of
solids, and the open line bypass affect.
A significant problem is usually encountered when
dealing with the production of heavy oil from an unconsolidated
formation when a long, horizontal or deviated slotted liner is
utilized. Briefly, when the liner penetrates clean sand or
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shale zones, fine sand particles and bitumen which are
displaced during the recovery process form a series of flow
paths.
A further problem encountered in production from a
horizontal well relates to the control of the recovery process
when a long inclined or horizontal liner is introduced into the
tar sand formation. Injected and produced fluids move in and
out of the formation radially under the effects of a huff and
puff external action and/or under the effect of condensation
and flashing during thermal pumping of steam, a method referred
to generally as steam stimulation.
Hot water, liquid additives and multiphase fluids
that stay far from saturation,.are not moved rapidly as easily
as steam condensate which is near saturation. The only way to
assure optimum penetration of stimulating liquids and/or gases
in mixture, is by backing their injection with pressure. This
mechanism is, however, less effective than flashing conduction
thermal pumping.
In any tar sand substrate, the desired sweeping
effect between the injection and production points along a
horizontal well is reduced at a negligible fraction since the
2~ permeability to flow of an open line is usually many times
higher than the permeability of the formation. Therefore, when
hot fluids other than steam are injected, the formation around
the previously stimulated liner in a cyclic steam injection, is
cooled down. This results since only a very small fraction of
fluids will be able to penetrate the formation.
The delicate balance between flow of hot stimulating
fluid, and heat transfer, will eventually further reduce the
actual flow rate into the formation to a very small
insignificant area around the slotted perforated liner.
It is found therefore that if the horizontal well is
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able to radially distribute the injected steam during the
stimulation step a reasonable, positive sweeping process can be
maintained along the well. The long horizontal liner will tend
to allow the hot fluids to bypass, thereby overrlding the
S formation during axial flow between the lnjection and producing
points along the liner.
There exists therefore an unfilled need for a system
which will make a long horizontal or devia~ed well, into a more
effectual system. Further, the well should be capable of
better controlling both axial, and radial inflow-outflow of
fluids.
In one embodiment of the presently disclosed
invention, a highly deviated, or substantially horizontal
wellbore is drilled to penetrate a tar sand formation. The
wellbore can extend substantially through the center of the
formation or along another appropriate level. A network of
similar deviated wells of identical construction can be
similarly drilled into the ~ormation.
The particular spacing of wells and their arrangement
will depend to a large degree on the size and the
characteristics of the particular formation. One embodiment of
the invention provides more than one well which extends through
a substrate and which will penetrate the formation at an
inclined alignment. Thereafter it can extend in a
substantially horizontal disposition through the hydrocarbon
productive layer.
To overcome the aforementioned pr~blems in producing
viscous hydrocarbons from a formation and in particular from a
tar sand environment, there is presently provided an elongated,
perforated well liner which is registered in a wellbore
disposed within the subterranean hydrocarbon producing layer.
A well head at one end of the liner permits pressured
introduction of a stimulating fluid to the substrate.
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An elongated fluid conduit is positioned in the
liner, extending longitudinally thereof and having a discharge
opening adjacent to the liner remote end. A diverter bed of
randomly disposed metallic fibers surrounds a portion of said
conduit to form a variable length, quasi-penetrable barrier in
the liner. The diverter thereby segregates or separates the
liner into injection and production segments or compartments.
The barrier bed is progressively lengthened as the process
proceeds whereby to assure a thorou~h thermal sweep of the
formation along the well liner.
It is an object of the invention therefore to provide
an improved means and method for producing hydrocarbon fluids
from a substrate that requires thermal stimulation. A further
object is to provide a well completion which is capable of
providing an efficient sweep of the surrounding substrate by
controlled introduction of stimulating fluid to the latter. A
still further object is to provide a well completion in which a
variable length diverter or quasi-barrier is utili2ed to most
effectively distribute a hot stimulating fluid into the
substrate whereby to provide a more efficient outflow of a
hydrocarbon aqueous emulsion.
- DESCRIPTION OF THE DRAWINGS
Figure 1 is an elevation view in partial
cross-section of a well of the type contemplated.
Figure 2 is a schematic, segmentary view of the well
shown in Figure 1.
Figure 3 is a cross-sectional view taken along line
3-3 of Figure 1.
Figure 4 is a segmentary view in cross-section taken
along line 4-4 of Figure 3.
In achieving the foregoing objectives, there is
presently provided a method of producing from, and a well
completion which is used in a substrate or layer which
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releasably holds a hydrocarbon fluid. An example of the latter
comprises a tar sand type of environment wherein a hydrocarbon
such as bitumen is releasably held within a mass of
unconsolidated sand particles.
Referring to the drawings, a wellbore 10 of the type
contemplated is shown which enters the ground vertically, or
preferably at an angle to the surface 11. Wellbore 10 is
initially spudded through the overburden 12 which overlies the
productive or tar sand layer 13.
Thereafter, partway through overburden layer 12, bore
10 is deviated in a manner that at least a segment of it Iies
in a generally horizontal relationship with respect to
hydrocarbon productive layer 13, as well as to the earth's
surface 11. Further, the well's horizontal segment is
preferably positioned at a depth to be adjacent to the lower
border of the generally horizontal layer 13. Following the
usual drilling practice, wellbore 10 is provided at its upper
end with a series of casing lengths 14 and 16, which are
affixed in place by cementing means.
An elongated well liner 17 is inserted through the
respective casings 14 and 16, and is supported in casing 16 by
a liner hanger 1~. The latter is structured to permit passage
o' bitumen emulsion andJor hot stimulating fluid therethrough
during the producing or the injection stages of the operation.
Liner 17 can be provided at its forward or remote end with
means to facilitate its being slidably inserted into and along
the wall of wellbore 10.
Structurally, liner 17 comprises a steel, pipe-like
member being perforated as required along that portion of its
wall which lies within tar sand layer 13. The perforations can
take the form of a series of holes 19 formed through the liner
wall. Alternately they can comprise slotted openings which
extend either longitudinally or peripherally about the liner.
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Further, said perforations can be formed either before or after
liner 17 is inserted into borehole 10 to perform their
function.
In any event, liner openings or perforations 19 are
adequate to allow the discharge of pressurized heating medium
therethrough and into the adjacent tar sand containing
substrate 13. Further, they allow the return flow or the entry
of a hot, aqueous bitumen mixture through ~he same wall
openings after said mixture achieves a flowable state.
In one embodiment, the forward or remote end OI liner
17 is provided with a panel or plate 21 which defines a
substantial barrier and partial closure to the end of the
liner. Said panel means is disposed normal to the longitudinal
axis of the liner and fastened in place by peripherally
arranged screws, bolts, or like fastening means 22.
An elongated, fluid carrying conductor or conduit 23
is disposed internally of liner 17. Said conductor can rest on
the liner inner wall and is preferably fixed at its remote end
by clamping means 24 which engages flange 26 at the conduit
open end.
Conductor 23 is constructed of continuous tubing or
alternately of pipe lengths which are interconnected end to end
at smooth connecting joints. Conduit 23 is capable of carrying
a pressurized stream of hot stimulating fluid such as steam,
hot water, or either of said elements having appropriate
chemicals intermixed therewith to facilitate the producing
process. The condition of the injected fluid will depend to a
large extent on the composition and character of the substrate
13.
The upper external ends of the respective liner 17
and conductor 23 are provided with a normal closure means such
as a well head 27. The latter, generally includes regulating
valves 28 and 29 which are operable to permit selective and
controlled communication of the individual liner 17 passages
with a source of stimulating fluid 31.
Conductor 23 is by and large unsupported along its
length in the liner 17. However, the remote end of the
conductor as noted is fixed in place adjacent panel 21 which
forms a closure to the liner end.
As seen in Figure 1, panel 21 is provided with a
split, multi-component bracket 24 which depends from the panel
inner face. Said bracket 24 includes an in-turned rim 32 which
is adap~ed along its face to engage a flange 26 formed about
the periphery of conduit 23. Thus, as a pressurized hot
lS stimulating fluid is discharged from the open end of conduit
23, it will be free to fill the injection chamber 34 and
thereafter to penetrate the surrounding formation by way of
perforation 19.
Referring to Figures 1 and 2, conduit 23 is provided
for part of its overall length with an enclosing flow diverter
36. Said diverter is comprised of a series of individual
filter-like diverter units 36a and 36b which are disposed
contiguous with or in close contact with each other within
liner 17. Diverter 36 functions as a quasi-barrier ~o direct a
stimulant such as steam from the injection chamber 34, and into
the surrounding substrate adjacent to the liner.
As hereinafter noted, diverter 36 will pass limited
minor amounts of the steam, while urging the major portion
thereof into the formation.
Over a period of operating time, the hot pressurized
steam will penetrate the formation 13 along liner 17 to soften
retained bitumen. It will further cause a bitumen-water
emulsion to form. This latter emulsion under the built-up
pressure within the formation will not only penetrate the tar
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sand and soften the bitumen, but will gravitate toward the
lower pressure producing compartment 37 of liner 17.
Referring to Figure 2, as the bitumen emulsion is
urged by built up pressure toward liner 17, it will establish a
series, or network of flow paths 38. The latter are created by
voids in the tar sand which result from evacuation of the
retained bitumen. After a sustained period of bitumen emulsion
production, the stimulating steam will pass directly through
the established flow paths 38. It will thereafter flow
directly into production segment 37 and out well head 27,
thereby minimizing the effectiveness of the steam.
It is necessary at this phase of the operation to
alter and extend the established flow paths 38 so that they
penetrate the formation closer to the liner well head 27. This
is achieved by lengthening diverter 36, whereby to preserve the
length and the volume of injection compartment 34, and to
concurrently reduce the length and volume of the production
segment 37.
This alteration in operating conditions is
effectuated by positioning additional diverter units as 36a,
adjacent to the original diverter member 36. Thus, the latter
will extend overall for a greater distance, and along liner 17
toward well head 27.
In the embodiment of Figures 1 and 3, the diverter is
comprised of a series of cylindrical units having a central
opening 39 which is capable of slidably registering onto the
conductor 23. As each successive diverter unit is applied to
the upper end of conductor 23, it is urged downwardly along the
wall of liner 17, and into direct contact with the diverter
units already in place.
The extended diverter will accomplish two purposes.
First, because of its quasi-pervious nature, it will cause most
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of the stimulating steam to pass from injection segment 34,
into the formation 13. Secondly, since the diverter is in
contact with the liner 17 walls, it functions as a detriment to
passage of bitumen emulsion which might flow toward the
diverter-occupied portion of liner 17. Stimulating steam will
thereby tend to e~tend flow paths i8 toward the liner
production segment 37.
Each diverter 36 section is comprised of a
cylindrical shaped mass or body 41 of randomly disposed
metallic fibers or fibrules. The fibers are compacted and
maintained in place onto a core piece 41 to achieve a
predetermined density. Thus, the passages defined between the
compressed fibers will form a quasi-barrier to thermal
stimulating medium whereby to throttle, and not entirely
prevent the flow of said heating medium into and through the
diverter.
As seen in Figure 1, the diverter 36 outside diameter
is sufficient to be slidably received not only along central
conduit 23, but also along the inner wall of liner 17. Thus,
as the respective diverter sections 36a, 36b, etc. are
sequentially urged into contact with the previously positioned
diverter, the aggregate unit will substantially fill the
annulus defined between the inner wall of liner 17 and conduit
23.
Each diverter unit as noted is basically cylindrical
in configuration. This shape, however, is provided to most
readily accommodate the open annular passage defined between
the adjacent liner 17 and central conduit 13. Further, while
the compacted fibrous mass is such as to provide a desired
density, the overall mass is nonetheless yieldable to permit
slidable insertion into the liner 17 as above noted.
Structurally, diverter 36 is formed and fabricated to
a desired shape, and to remain substantially the same shape
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under expected operating conditions of high temperature and
pressure. The random fibers are therefore comprised of a
temperature resistant metal such as steel, and preferably
stainless steel. Similarly, when an internal core or sleeve 39
is utilized, it, too, is fabricated of steel to afford
structural integrity. A diverter barrier formed as described
herein will be capable of resisting thermal deformation and
loss of efficiency even under most arduous thermal stimulating
conditions.
Operationally, diverter 36 is preferably fixedly
assembled onto conduit 23 at the time the latter is initially
registered in and connected to liner 17. As herein noted, the
remote end of conductor 23 is connected by means of flange 26
and its mating bracket 24 on panel 21 to properly position the
conduit.
With diverter 36 fabricated to a desired length and
initially positioned on conduit 23, the latter, together with
liner 17, are inserted as a unit into a borehole 10.
Thereafter as production of bitumen proceeds as herein noted,
the outflow of bitumen emulsion will normally vary as a
function of the volume and quality of steam which is injected
into the formation.
After a period of operation, the stimulating steam
will tend to follow the flow paths 38 and enter liner 17,
thereby avoiding the extension of said flow paths into the
areas from which additional bitumen emulsion can be produced.
This phenomenon will be noted at well head 27 by monitoring the
amount of steam which is produced.
When it becomes apparent that an excessive amount of
steam is exiting from the liner, diverter 36 will be extended
to in effect maintain the size of the injection segment 34 in
the liner, while reducing the volume of the production segment
37.
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This is achieved as herein noted by positioning one
or more additional diverter segments 36a and 36b onto conduit
23. The diverter sections can be urged downwardly and guided
by conduit 23 into contact with the initially placed diverter
36.
The number of diverter segments so added is
sufficient to extend the length of the overall diverter 36 and
reduce the volume of producing segment 37 thereby permitting
the formation of new flow paths as extensions of the originally
formed flow paths 38.
The additional diverter segments can be positioned in
any one of a number of ways whereby the aggregate diverter 36-
will be comprised of a series of continuously disposed divertersegments. They can, for example, be propelled or urged along
conduit 23 by any means appropriate to the operation. Such a
means can, for example, comprise one or more elongated,
retractable push rods.
Further, the packing of the filter mass of the added
diverter segments can be designed to achieve a desired density.
This will allow -the steam penetration into the barrier to be
regulated.
With the now extended diverter in place, the initial
operation of injecting stimulating steam through conduit 23 can
be resumed. As herein noted, the steam rather than entering
liner 17 along that section of liner 17 which encloses the
diverter, will tend to bypass said section and allow the
bitumen emulsion to enter the shortened production segment 37.
Although modifications and variations of the
invention may be made without departing from the spirit and
scope thereof, only such limitations should be imposed as are
indicated in the appended claims.
